1. Field of the Invention
The present invention generally relates to a centering apparatus which centers a disk to a rotation center member such as a shaft or hub, and more particularly to a centering apparatus suitable for an operation in which a disk to be provided in a magnetic disk drive is centered to a shaft and attached thereto in order to record servo track information on the disk.
Generally, servo track information is recorded on disks, which are recording media of a magnetic disk drive. Usually, heads are positioned on the disks using a length measuring device in a state in which the magnetic disk drive is completely assembled. Then, servo track information is recorded on the disks.
However, the above recording operation has the following disadvantages.
First, it is very difficult to improve the precision of the servo track information in order to write servo track information by using the heads provided in the magnetic disk drive and thus improve the recording density. Second, the servo track information is recorded on all the disks by using all the heads of the magnetic disk drive and thus it takes a long time to complete the recording operation. This also increases the production cost.
An improvement directed to overcoming the above first disadvantage has been proposed in which servo track information is recorded on a single disk by means of an exclusive servo track information recording apparatus. The single recording disk is then installed in the magnetic disk drive. A plurality of such recording disks are prepared and each of the disks is then installed in a respective magnetic disk drive. Hence, the second disadvantages can be simultaneously overcome.
However, the above improvement has the following disadvantages. Disks are attached to a shaft or hub of the servo track recording apparatus with a certain eccentricity. Similarly, disks on which servo track information has been recorded are attached to hubs of the magnetic disk drives with a certain eccentricity. Generally, a gap approximately equal to 50 xcexcm to 100 xcexcm is provided between the edge of the opening of the disk and the outer circumference of the hub or shaft in order to facilitate an engagement operation in which the disk is engaged with the hub or shaft. If there is no eccentricity, the opening of the disk is evenly spaced apart from the outer circumference of the disk.
If an eccentricity occurs in a case where the disk is loaded to the servo track information recording apparatus and the servo track information is recorded thereon or in a case where the disk is loaded to the magnetic disk drive, the trace along which the servo information track has been recorded on the disk has an eccentricity with respect to the shaft or hub of the magnetic disk drive in the assembled state. The above eccentricity of the trace of the servo track information requires that the read/write head is operated with the same eccentricity with respect to the shaft or hub and thus degrades the read/write performance. Further, the above eccentricity causes a vibration during rotation and also degrades the read/write performance.
In order to reduce the eccentricity, the above-mentioned gap can be reduced. However, this requires each component to have a higher precision and thus increases the production cost. Further, the engagement operation becomes complex. It will be noted that the above problem occurs in all apparatus in which a disk is attached to a shaft or the like and is then centered.
It is a general object of the present invention to provide a centering apparatus and method in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a centering apparatus and method in which a disk having an opening can be centered about a shaft, hub or the like without eccentricity so that the edge of the opening of the disk can evenly be spaced apart from the outer circumference of the shaft or the like.
The above objects of the present invention are achieved by a centering apparatus for centering a disk about a center member, comprising a plurality of pairs of actuator units, the actuator units of each of the pairs facing each other through the disk, each of the actuator units having a member which moves linearly and can come into contact with the disk.